In processes where metal surfaces come in contact with water, whether as liquid water or humid air, there is always the danger of corrosion. This is particularly problematic when the metal itself is prone to corrosion and is not coated.
Examples of metals prone to corrosion are found in stamped metal car parts made from ferrous alloys, abraded surfaces such as machined steel parts, and machine components made from cast iron. Although corrosion inhibitors (or anticorrosive agents) have been known for many years, most are still inadequate. One key inadequacy is that of water solubility. Most corrosion inhibitors are produced from long chain fatty acids and derivatives and often have poor aqueous solubility. This is especially problematic when the metal surface contacts both water and oil, such as in oil and gas production, petroleum processing, and metal working applications. Petrochemical processing itself presents a wide array of challenges for corrosion inhibitors including cooling systems, refinery units, pipelines, steam generators, and oil or gas producing units.
In order to reduce the rate of corrosion of metals (such as metal vessels, equipment metal parts, equipment surfaces, pipelines, and equipment used to store the fluids), especially those containing iron, corrosion inhibitors are typically added to the fluid contacting the metal. The fluid may be a gas, a slurry, or a liquid.
Traditional solvents for cleaning metal and metal parts, such as mineral spirits and kerosene, have been replaced in recent years by aqueous formulations due to concerns about volatile organic carbons (VOCs). This move toward water-based formulations for cleaning metal parts is not without problems. Water does not solubilize grease or oily residues easily, and water itself can markedly increase the corrosion of the metal parts themselves. In addition, formulations are typically used as microemulsions, which require the use of additional surfactants for stabilization during the cleaning process. Morpholine is frequently used in these cleaning formulations to provide corrosion protection. However, morpholine does little to contribute to cleaning, and does not stabilize the microemulsion, since it is not a good surfactant. Furthermore, morpholine is a regulated product, since it may be used to prepare illicit drugs.
Quaternary ammonium compounds have found limited use as corrosion inhibitors. U.S. Pat. No. 6,521,028 discloses the use of particular pyridinium and quinolinium salts, in either propylene glycol or propylene glycol ether solvents, as corrosion inhibitors.
U.S. Pat. Nos. 6,080,789, and 6,297,285 disclose the use of quaternary ammonium carbonates as disinfectants.
U.S. Pat. No. 4,792,417 discloses a composition for inhibiting stress corrosion of stainless steel in contact with aqueous and/or polar organic solutions which contain chloride ions and optionally cuprous ions. The composition comprises an aqueous or polar organic solution of a particular quaternary ammonium alkylcarbonate or quaternary ammonium benzylcarbonate.
There is still a need for corrosion inhibitors that possess good affinity for metallic surfaces and are both water and oil soluble. Additionally, there is a desire for new corrosion inhibitors that add cleaning and or surfactant capability. Corrosion inhibitors that also afford antimicrobial protection to the finished formulation to which they are applied would be particularly advantageous.